1. Technical Field
The following description relates to a magnetic field communication method in low frequency band for managing node with low power consumption which enhances performance and efficiency of a magnetic field area network in the low frequency region.
2. Description of the Related Art
As is generally known, a low frequency band magnetic field area network (MFAN) is a wireless communication network for transmitting and receiving information using magnetic field signal in the low frequency region between 30 KHz and 300 KHz. The center frequency of a wireless communication is 128 KHz and binary phase shift keying (BPSK) is commonly used as a modulation method. Manchester coding and non-return-to-zero level (NRZ-L) coding are used for diversifying data rates, and several Kbps data rate within several meters can be provided.
Meanwhile, devices being participated in a MFAN are classified into two groups according to their role: MFAN coordinator (MFAN-C) and MFAN node (MFAN-N). Only one MFAN-C exists per one MFAN, and the MFAN includes one MFAN-C and a plurality of MFAN-Ns that are connected thereto. MFAN-C manages connection and disconnection of MFAN-Ns. MFAN adopts time division multiple access (TDMA) method. MFAN-C manages connection inside of the MFAN; time resources are distributed according to the judgement of the MFAN-C whenever MFAN-Ns are connected thereto. MFAN technologies described above can be applied to the service areas such as sensor networks, home networks, constructions, transportations, etc.
In relation to such MFAN, the applicant of the present invention had filed a Korea Patent Application No. 10-2008-131920 entitled “PHY layer of low frequency band based on wireless magnetic field communication (hereinafter referred to as ‘prior application”). Above-described prior application suggests a method for configuring a physical layer (PHY) that enables wireless communication by using a variable data rate or selecting an appropriate coding method in accordance with the neighboring environment considering the problems of conventional MFAN wherein efficient communication cannot be performed due to the fixed data rate or the adopted coding method. In the above mentioned prior application, the frame format of the physical layer includes three major elements: a preamble, a header, and a payload. When a packet is transmitted, a preamble is transmitted first followed by transmission of a header, and then a payload is finally transmitted. Transmission is performed from the least significant bit (LSB). The preamble, shown in FIG. 1, performs identical function like a start-of-frame (SOF) field of a conventional general request or response format. Such preamble is sequentially including bits from the LSB to the most significant bit (MSB). For example, it can include sequences whose length is assigned by a user including a 0-bit, 4-bit, 8-bit or 12-bit “0” sequence, a 4-bit “0000” sequence, and a 4-bit “1010” sequence. Eventually, the preamble will include a 4-bit “0000” sequence and a 4-bit “1010” sequence because there may be no user assigned sequence when the user assigned sequence has a 0 bit.
In a conventional low frequency band MFAN communication method, all the MFAN-Ns perform wake-up functions by detecting the carrier frequency transmitted from the MFAN-C.
As described above, according to the conventional low frequency band MFAN communication method, power consumption of the MFAN-N increases since it is awakened by detecting the carrier frequency not by a separate wake-up signal, for example, it is awakened unnecessary and frequently by the carrier frequencies transmitted to the MFAN-C by other MFAN-Ns.
Furthermore, according to the conventional low frequency band MFAN communication method, it has the disadvantage of increasing power consumption since there is no adequate procedure for stopping the operation even though errors are repeatedly occurred during the operation of the MFAN-C.